More than 200 organic compounds have been detected in breath exhaled from humans. Volatile Organic Compounds (VOCs) such as alcohols, aldehydes, hydrocarbons, and ketones are constituents of human breath at parts per trillion (ppt) to parts per million (ppm) levels. For a more complete discussion of VOCs in human breath, see, for example, A. Manolis, Clin. Chem. 1983, Vol. 29, p 5; J. Fenske et al., J. Air Waste Management Assoc., 1999, Vol. 49, p. 594; and R. Sachs et al., Anal. Chem. 2003, Vol. 75, p 2231, all three of which are incorporated herein by reference. The concentrations of VOCs in breath are representative of their concentrations in blood through rapid gas exchange at the blood/gas interface in the lungs. By analyzing human breath, one can probe the general health of an individual and uncover exposure(s) to drugs or environmental pollutants. Both volatile organic compounds, such as solvents, can be of concern in environmental and industrial contexts.
Very few VOCs in breath are able to be measured (quantitatively or qualitatively) by methodologies suitable for routine evaluation. This is because most VOCs in breath are present at very low concentrations so that preconcentration techniques coupled with complicated separation and detection methods, such as gas chromatography and mass spectrometry, generally would be used to determine their presence. This type of breath analysis methodology requires technical skill, is expensive, and is generally not portable so that it is not practically employed in the field. One notable exception is the determination of Blood Alcohol Concentration or Blood Alcohol Content (BAC) by breath analysis for the VOC analyte ethanol.
Ethanol is a by-product of respiration and is found to be in human breath whether or not an individual has been consuming it. Elevated levels of ethanol necessary for behavioral impairment, in most circumstances, is only possible by ingestion and is a matter of law. BAC is a measurement of the mass of alcohol (ethanol) in a given volume of blood, mg (milligrams) ethanol per 100 ml (milliliters) blood. For instance, 0.04 BAC implies a concentration of 40 mg of alcohol in 100 mL (milliliters) of blood In the U.S., BrAC is specified as BAC/2100. Ethanol at 34° C. is in equilibrium at blood at a ratio of roughly 2100:1 based on the distribution of alcohol in equilibrium with the blood in the deep part of the lungs. In other words, 2100 ml of air in the deep parts of the lungs contain the same amount of alcohol that is present in 1 ml of blood Indirectly measuring BAC through breath analysis (BrAC) can be accomplished by infrared spectroscopy (IR), chemical reactions to produce color changes, semiconductor sensors, and fuel cells (FCs). See, for example, further discussion of these approaches in Choi et al., Sensors and Actuators B, 2000, Vol 67, p 194; P. Millet et al., J. Applied Electrochem., 1996, Vol. 26, p 933; A. Jones, “Fifty years on—looking back at developments in methods of blood- and breath alcohol analysis,” International Conference on Alcohol, Drugs and Traffic Safety, May 22-26, 2000; and N. Pausson et al., Forensic Science International, 1999, Vol. 105, p 95, all four of which are incorporated herein by reference.
Sensitivity and selectivity to ethanol vary for all BrAC methodologies mentioned above. In addition, BrAC measurements are subject to variability due to the difficulties in obtaining consistent breath samples. Infrared spectroscopy and FCs are utilized extensively, either alone or in tandem, in evidentiary BrAC measuring instruments. At present, fuel cells are the sensor technology of choice in portable BrAC measurement instruments, mainly due to the physical constraints on hardware design. Two examples of portable BrAC measurement instruments are field sobriety measurement devices used by law enforcement and interlocks used to prevent repeat offenders of driving while intoxicated from starting their vehicle if they have a BrAC over a selected value.